The invention relates to improved adhesive formulations and to methods for attaching a semiconductor chip to a nozzle plate for an ink jet printhead.
Ink jet printers continue to evolve as the technology for ink jet printing continues to improve to provide higher speed, higher quality printers. The improvement in speed and quality does not come without a price, however. The ink jet pens of such printers are more costly to manufacture because of tighter alignment tolerances which must be met for the operative parts of the printers. One area of increased criticality is the alignment tolerance between the nozzle plate and semiconductor chip components of the ink jet pen.
During the manufacturing process an ink jet pen, a nozzle plate is aligned to a semiconductor chip so that heater resistors used for heating the ink on the semiconductor chip align with nozzle holes on the nozzle plate. Misalignment between the heater resistors and the nozzle holes has a disadvantageous effect on the accuracy of ink droplet placement of ink ejected from the nozzle holes to the print media. Heater resistor and nozzle plate alignment also has an effect on the mass and velocity of the ink droplet ejected through the nozzle hole.
There are multiple manufacturing steps required to produce an ink jet pen. First a nozzle plate is attached to the semiconductor chip after aligning the nozzle plate and chip to one another. The TAB circuit or flexible circuit is then electrically connected to a semiconductor chip using a wire bonding or TAB bonding process. The resulting nozzle/plate chip and circuit assembly is then attached to a cartridge body in a chip pocket thereon using a die bond adhesive. Finally the TAB circuit or flexible circuit portion of the assembly is adhesively attached to the cartridge body. Because of the multiple adhesives used for making the ink jet pen, there are several curing steps required during the assembly of the pen components. With each assembly and curing step there is an opportunity for component misalignment to occur.
Despite advances made in the art manufacturing ink jet pens for ink jet printers, there remains a need for improved adhesive formulations and methods which provide alignment of the pen components as required for higher quality printers.
With regard to the foregoing and other objects, the invention provides an adhesive formulation for tacking and holding a nozzle plate in alignment on a semiconductor chip for an ink jet pen of an ink jet printer. The adhesive formulation includes a multifunctional epoxy material, a difunctional epoxy material, a fumed silica viscosity control agent, an imidazole-based thermal initiator and a mixed aryl sulfonium salt photoinitiator.
In another aspect the invention provides a method for making an ink jet pen for an ink jet printer. According to the method dots of a UV and thermally curable adhesive are applied to at least two diagonally opposed corners of a nozzle plate or semiconductor chip. The adhesive includes a multifunctional epoxy material, a difunctional epoxy material, a fumed silica viscosity control agent, an imidazole-based thermal initiator and a mixed aryl sulfonium salt photoinitiator. After applying the adhesive dots to the nozzle plate or semiconductor chip, the nozzle plate and semiconductor chip are aligned to one another to provide a nozzle plate/chip assembly. At least a portion of the adhesive dots is exposed to actinic radiation in order to cure an amount of the adhesive sufficient to substantially maintain alignment between the nozzle plate and semiconductor chip during subsequent curing and assembly steps. The nozzle plate/chip assembly is then heated to a temperature sufficient to cure any portion of the adhesive dots not cured by exposure to the actinic radiation.
In yet another aspect the invention provides a pen for an ink jet printer. The pen includes a cartridge body containing one or more printheads attached thereto. Each printhead includes a nozzle plate, a semiconductor chip attached to the nozzle plate and a flexible circuit or TAB circuit attached to the semiconductor chip. The flexible circuit or TAB circuit contains electrical traces and electrical connections from the traces to semiconductor chip. A UV and thermally curable adhesive is used for tacking the nozzle plate and the semiconductor chip to one another. The adhesive contains a multifunctional epoxy material, a difunctional epoxy material, a fumed silica viscosity control agent, an imidazole-based thermal initiator and a mixed aryl sulfonium salt photoinitiator.
An advantage of the compositions and methods according to the invention is that ink jet pens may be assembled and critical alignment between functional parts may be maintained throughout the assembly process. The adhesive formulation described herein is particularly useful for tacking and holding a nozzle plate to semiconductor chip after aligning the nozzle plate to the chip. Because of the quick cure of the UV curable portion of the adhesive, the alignment, once set, is substantially maintained throughout subsequent high temperature heating and/or pressure curing steps of the manufacturing process. The adhesive provides a useful combination of adhesive tack and viscosity in its uncured state and enables substantially complete cure of the adhesive by both UV and thermal curing methods despite the presence of areas of the nozzle plate/chip assembly which cannot be adequately cured by UV curing methods alone.